172 



CCELENTERATA. 



the Hydrozoa. This conclusion has been confirmed by the 

 more recent and more complete researches of Mr Moseley. 

 At the present day, Millepora contributes largely to the 

 formation of coral-reefs ; but little is known of its distri- 

 bution in past time. The genus has been detected in the 

 Tertiaries, and allied forms (Porosphcera) occur in the Chalk. 

 The Tertiary genus Axopora is apparently allied to Millepora, 

 but the tubes inhabited by the larger zooids are traversed 





Fig. 65. A, Portion of a mass of Millepora alcicornis, of the natural size ; B, Portion of 

 the same, cut open vertically to show the larger tabulate tubes (p, p), and the spongy 

 coenosarcal skeleton (c, c) enlarged ; c, Small portion of the surface, enlarged to show the 

 larger and smaller openings (p and c) inhabited by the different zooids, and the reticulated 

 calcareous tissue of the skeleton ; D, Part of a tentacular polypite, enlarged, showing two 

 whorls of knobbed tentacles. (A, B, and c are after Milne-Edwards and Haime ; D is after 

 Martin Duncan and Major-General Nelson.) 



by a large fasciculate " columella " or central rod. According 

 to Mr Carter, the ancient and widely distributed forms re- 

 ferred to Stromatopora and to allied genera are really closely 

 related to Millepora, but this conclusion cannot be accepted 

 without further evidence. 



We must also mention here the extraordinary forms known 

 as the Stylasteridce, which have been shown by Mr Moseley 

 to be true Hydroids, producing a calcareous corallum. But 

 brief notice, however, can be given to the group, since there 

 is at present only one known fossil example of it (Disticho- 



